Alpha and beta diversity and distribution pattern of millipedes (Myriapoda Diplopoda) along an altitudinal gradient in Southern Cameroon rainforest

Mountainous regions serve as critical ecosystems that promote endemism and serve as biodiversity hotspots, supporting a wide array of species, including millipedes. As one of the most important bioindicator groups, millipedes are particularly sensitive to habitat loss and tend to thrive in specific ecological niches. This study investigates the influence of altitudinal gradient on the community structure and assemblages of millipedes in southern Cameroon rainforest. Millipedes were sampled using a combination of pitfall traps, quadrat sampling, and litter sifting across three distinct elevational zones and vegetation types (0–400 m, 401–800 m, and 801–1200 m above sea level). A total of 994 individuals representing 71 species, 4 orders, 12 families, and 41 genera were recorded. The order Polydesmida was the most abundant and diverse (comprising 60.56% of the total sample and 35 species), followed by Spirostreptida (28.67% and 31 species) and Spirobolida (9.25% and 4 species). Cryptodesmidae was the most abundant family, while the least abundant was Spirostreptidae. The most abundant species was Aporodesmus gabonicus (29.38%), followed by Kartinikus colonus (7.75%) and Aporodesmus falcatus (5.73%). Along the altitudinal gradient, the millipede diversity increased slightly from lower level (H1’ = 1.32±0.15) (0-400 m asl) to transitional level (H2’ = 1.56±0.13) (401-800 m asl), and reached a maximum in upper level (H3’ = 1.98±0.18) (801 m to 1200 m asl). This distribution pattern of millipede in diversity suggests biotic homogenization as main factor leading to the weak dissimilarity of species between different altitudinal zones and the replacement of habitat specific species by opportunist or cosmopolitan species. This study provides valuable insights into the biogeography of millipede species along altitudinal gradients and offers essential information that could inform future conservation strategies aimed at preserving these sensitive ecosystems.